There are many cases where a water-repellent stain-proofing coating film is formed on surfaces of various substrates, for example, stone, concrete, metal, plastic, wood and the like to prevent adhesion of stain and easily remove stain. Such a stain-proofing coating composition is roughly classified into (1) an inorganic coating composition mainly comprising a silicone compound (for example, JP64-45411A, etc.), (2) a curable coating composition comprising a fluorine-containing resin and an acrylic resin (for example, JP60-21686B, JP57-23662A, JP63-264675A, JP5-25422A, etc.), (3) a coating composition prepared by mixing a stain-proofing silicon-containing low molecular weight compound to a coating film forming resin (for example, JP1-51477A, JP9-78029A, WO98/22530, JP5-339538A, JP11-29722A, JP2-75649A, JP10-88065A, etc.) and the like. When forming the inorganic coating film of above (1) on a substrate surface, it is difficult to carry out coating uniformly continuously over the substrate surface, and a long-lasting stain proofing effect cannot be expected.
In the method of coating a water- and oil-repellent resin of above (2), strength of a coating film itself can be obtained but a stain-proofing effect is insufficient.
The coating composition of above (3) prepared by mixing a stain-proofing silicon-containing low molecular weight compound to a coating film forming resin is intended for compensating for problems of (1) and (2) above, but it is difficult to uniformly disperse the silicon-containing low molecular weight compound in the coating film forming resin and further to concentrate the silicon-containing low molecular weight compound around the coating film surface, and it is particularly difficult to maintain the silicon-containing low molecular weight compound around the surface for a long period of time. A coating composition providing a coating film which can maintain a stain-proofing effect for a long period of time has not yet been found out.
On the other hand, there have been trials to obtain a stain-proofing effect of a coating film surface by making the surface hydrophilic but not water- and oil-repellent. For example, WO97/11130 discloses a coating composition comprising a fluorine-containing resin as a coating film forming component and a tri-functional or tetra-functional fluorine-containing silicate compound (having 3 to 4 hydrolyzable groups) as a stain adherence inhibitor. However this coating composition is used for achieving a stain-proofing effect by hydrolyzing a fluorine-containing silicate concentrated around the coating film surface and making the surface hydrophilic with a hydrophilic group after hydrolyzation. A group having fluorine is a hydrolyzable group, and is released by hydrolyzation and does not exist around the coating film surface.
Further coating compositions for enhancing a property of preventing adherence of snow and ice and a property of sliding snow but not for giving a stain-proofing property have been proposed (for example, JP4-85369A, JP58-132073A, etc.). JP4-85369A discloses that a silicone- or fluorine-containing water-repellent agent having no functional group and a lubricant are mixed to a hydroxyl-containing chlorotrifluoroethylene copolymer. Also JP58-132073A discloses that a silicone oil is mixed to an air drying vinyl resin or acrylic resin having no functional group. However even if a coating film is formed by using the compositions disclosed in those patent publications, since a water-repellent agent, lubricant and silicone oil in the coating film bleed or are released from the film surface, there is a problem that a property of maintaining the effects thereof is insufficient.
An object of the present invention is to provide a coating composition which can make a coating film surface water- and oil-repellent and can maintain a stain-proofing effect, particularly stain removability and a property of wiping off stain for a long period of time even in case of outdoor use.